Apigenin and tt-farnesol, were identified as potentially novel natural anti-caries agents (Koo et al., 2002b; c). Both agents exhibited cariostatic properties in rats without significant effects on the animals' oral flora. Apigenin is a potent inhibitor of glucosyltransferases (GTFs), both in solution and on a surface (60-95% inhibition at 1.33mM), and without effect on bacterial growth, tt-Farnesol, in contrast, affects the growth rate and metabolism of mutans streptococci biofilms by disrupting the membrane function. The aim of the proposed study is to evaluate the effects of the combination of apigenin, tt-farnesol and fluoride on the formation and composition of mutans streptococci biofilms in vitro, and on caries development in rats. [unreadable] [unreadable] Fluoride is a clinically proven anti-caries agent; its main effect is to interfere physicochemically with caries development. However, fluoride has antibacterial activity, and in addition, may interfere with GTF production (Bowen and Hewitt, 1974). Our hypothesis is that the association of the natural agents may enhance the anti-caries effect of fluoride by synergistically diminishing the virulence factors of mutans streptococci involved in the pathogenesis of dental caries. The rationale for this study is that the combination of the therapeutic agents will reduce the formation and virulence of cariogenic biofilms by (a) inhibiting the synthesis of glucans, e.g., inhibition of the activity and production of GTFs; Co) reducing the acid tolerance, e.g., inhibition of F-ATPase; (c) reducing the acidogenicity, e.g., enhancing the access of fluoride into cells by increasing the bacterial membrane permeability. We will test our hypothesis using a series of experiments as follows: I) In vitro- By determining the effects of the combination of agents on (1) formation, (2) viability, (3) pH, and (4) polysaccharide and inorganic composition of mutans streptococci biofilms. Streptococcus mutans biofllms formed on hydroxyapatite disks will be used in this part of the investigation. The polysaccharide composition will be determined by a series of colorimetric assays, liquid scintillation counting and gas chromatography/mass spectrometry. The concentrations of fluoride will be determined using a fluoride-selective electrode, calcium will be analyzed by atomic absorption spectrophotometry and phosphorus will be determined colorimetrically. The pH of the biofilms will be measured using a Beetrode pH electrode. II) In vivo - By evaluating the ability of combination(s) of agents (selected from in vitro analyses) to reduce dental caries, and to affect the pH and the composition of plaque using our rat model. The outcome of this study may lead to new and effective therapeutic combinations interventions to prevent dental caries, and possibly other plaque related diseases by using novel compounds in association with a well-known anti-caries agent. [unreadable] [unreadable]